1. Field of the Invention
The present invention relates to a target for an X-ray generator which is particularly used for generating a high brilliance (intensity) X-ray, a method of manufacturing the same and the X-ray generator.
2. Description of the Related Art
There is a generally known X-ray generator, such as an apparatus using a filament as a cathode and using a target as an anode, wherein the filament is available as a thermal electron source and the target is an object with which electrons collide. A high voltage of several tens of kilo volts is applied between these cathode and anode so that fast electrons collide with the target, to thereby generate an X-ray.
A brilliance level (called X-ray intensity hereafter) capable of generating X-ray, can be given as a most basic performance of the X-ray generator, and various attempts have been made conventionally for increasing the X-ray intensity. In many cases, a value obtained by dividing an applied power (=applied voltage×applied current) by an area of an X-ray generation area (focal point) on the target, is used as a value showing the X-ray intensity, instead of directly indicating the X-ray intensity. This is because the intensity of the generated X-ray is substantially proportionate to the applied power per unit area. In this specification as well, the applied power per unit area is used as a value showing the X-ray intensity.
As mentioned above, X-ray intensity is determined by power applied per unit area of the target. Therefore, the X-ray intensity is increased by increasing the applied power per unit area. One of the keys to increase the applied power is how quickly heat produced by the collision of electrons can be dissipated from the collision area. Accordingly, various attempts focusing on that point have been made conventionally.
In order to dissipate heat efficiently from the collision area, many of the attempts are made to form a small or thin target material so that another material (thermal diffusion material) having a larger thermal conductivity than that of the target material is brought into contact with the target material (for example, see patent document 1). Namely, patent document 1 (Japanese unexamined patent application publication No. 8-115798) describes in paragraphs 0035 to 0036, as “example 1”, an example in which a through hole of 0.2 mm diameter is formed in the center of a polycrystalline diamond substrate 2 (heat conductivity 16.9 W/cm·K) having 10 mm diameter and 1 mm thickness, and the through hole is filled with metal Cu to form a target (anticathode 1), then a Cu film is formed on a rear surface, and a side face is brought into contact with a cooling holder 5 (FIG. 2).
Further, patent document 1 describes an example in paragraph 0044 as a comparative example 1, in which a metal copper film is vapor-deposited on a surface of a disc-shaped polycrystalline diamond substrate 32 having 10 mm diameter and 1 mm thickness to form a thin film target, with a side face in contact with the holder 5 shown in FIG. 2.